Comparative study of mechanical and electrical relaxations in poly(etherimide). Part 2

Calleja, R. Dı́az; Friederichs, S.; Jaime's, Catherine; Sanchı́s, M. J.; Belana, J.; Cañadas, J. C.; Diego, J. M.; Mudarra, M.

doi:10.1002/(sici)1097-0126(199805)46:1<20::aid-pi944>3.0.co;2-u

Cited by 20 publications

(16 citation statements)

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“…Figures 3 and 4 show the results of the dielectric loss in the frequency domain, at several temperatures, for LC95 without and with homeotropic alignment, respectively. The steep rise at low frequencies in Figs 3 and 4 is caused by electrical conductivity as previously proposed 18. In agreement with the Macdonald19 and Coelho20 models we consider two processes for the space charge relaxation: ohmic conduction and blocking electrodes.…”

Section: Resultssupporting

confidence: 82%

“…Equation (4) assumes, from an electrical point of view, a series coupling between bulk conductivity and interfacial contributions to the loss, but does not include dipolar contributions. To take dipolar contributions into account we could assume that they are in parallel with the bulk conductivity and both in series with the interfacial phenomena; this gives us a complicated expression for the permittivity (see Díaz‐Calleja et al ,18 eqn A28). To simplify the treatment we note that at the sight of the values of the parameters appearing in Tables 3 and 4, tanh( X D )/ X D is very low in comparison with ωτ ; for this reason, interfacial contributions can be ruled out from eqn (4).…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Dielectric relaxation studies on thermotropic side-chain liquid crystalline polymers

Garcı́a-Bernabé¹,

Díaz‐Calleja

2001

Polym. Int.

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Section: Resultssupporting

confidence: 82%

Section: Resultsmentioning

confidence: 99%

Dielectric relaxation studies on thermotropic side-chain liquid crystalline polymers

Garcı́a-Bernabé¹,

Díaz‐Calleja

2001

Polym. Int.

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“…It is also known that the loss factor of U1000 increases sharply for temperatures close to the glass transition temperature due to conductive processes [3]. In the case of thermally stimulated depolarization currents (TSDC) measurements, the relaxation of space charge is associated with the ρ relaxation, which appears at temperatures higher than the α relaxation, associated to the glass transition [4].…”

Section: Polyetherimide (Pei) Is An Amorphousmentioning

confidence: 84%

Sublinear dispersive conductivity in polyetherimides by the electric modulus formalism

Mudarra

Sellarès

Cañadas

et al. 2015

IEEE Trans. Dielect. Electr. Insul.

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Dynamic Electrical Analysis shows that the electrical properties of polyetherimide at temperatures above the glass transition are strongly influenced by space charge. We have studied space charge relaxation in two commercial grades of polyetherimide, Ultem 1000 and Ultem 5000, using this technique. The electric modulus formalism has been used to interpret their conductive properties. In both grades of polyetherimide, asymmetric Argand plots are observed, which are related to a sublinear power-law dependency (ω n with n<1) in the real part of the conductivity. This behavior is attributed to correlated hopping. The imaginary part of the electric modulus exhibits a peak in the low frequency range associated with conduction. The modelisation of this peak allows us to obtain the dependence, among other parameters, of the conductivity (σ 0 ), the fractional exponent (n) and the crossover frequency (ω p ) on the temperature. The α relaxation, which appears at higher frequencies, has also to be modeled since it overlaps the conductivity relaxation. The study of the parameters in terms of the temperature allows us to identify the ones that are thermally activated. The difference between the conductivity relaxation time and the Maxwell relaxation time indicates the presence of deep traps. The coupling model points out that the correlation of the ionic motion diminishes with temperature, probably due to increasing disorder due to thermal agitation.

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“…This formalism has been successfully applied to evaluate conductivity effects in polymers like polyethylene terephthalate,21, 22 nylon‐11,23, 24 polyether imide,25 and segmented polyurethanes 26–28. However, as we will show later, this representation is very useful in our case because it allows us to discriminate between conductive and dipolar relaxation better than in other representations, based on the greater weight of the high frequencies for the modulus 19…”

Section: Resultsmentioning

confidence: 99%

Electric modulus and polarization studies on piezoelectric polyimides

Gonzalo¹,

Vilas²,

Sebastián³

et al. 2011

J of Applied Polymer Sci

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The piezoelectric polymeric sensors and actuators are widely valued because of their low density, availability to obtain complex shapes, and easy processing among other characteristics. However, there are not many useful piezoelectric polymers. Aromatic polyimides are high‐performance polymeric materials characterized by thermal stability, chemical resistance, and excellent mechanical properties. Besides, some of these polymers have been reported as candidates to present piezoelectric properties. Our research focuses in the electric characterization of three piezoelectric amorphous aromatic polyimides, containing CN groups in different number and positions. The piezoelectricity in amorphous polymers is mainly due to the orientation polarization of the molecular dipoles, which is induced by the application of an external electrical field to a temperature over their glass transition temperature (Tg). Polyimides are measured by thermally stimulated depolarization currents and dielectric spectroscopy and the analysis of the dielectric data has been performed using the electric modulus formalism to separate conductive and dipolar processes. These measurements have evidenced that the frozen‐in polarization is mainly due to the dipole orientation of the dipolar CN groups, allowing us to understand in depth the mechanism of polarization that contributes to the piezoelectric properties. This will facilitate the obtention of materials with the best possible piezoelectric properties, comparable to those currently available but with higher mechanical and thermal performance. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

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Comparative study of mechanical and electrical relaxations in poly(etherimide). Part 2

Cited by 20 publications

References 0 publications

Dielectric relaxation studies on thermotropic side-chain liquid crystalline polymers

Dielectric relaxation studies on thermotropic side-chain liquid crystalline polymers

Sublinear dispersive conductivity in polyetherimides by the electric modulus formalism

Electric modulus and polarization studies on piezoelectric polyimides

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